This invention relates to the generation of trigger signals for a serial stream of bits which has a continuously repeating pattern and which has been formed by serializing a plurality of parallel streams The invention has particular, but not exclusive, application to the generation of trigger signals for a class of serial streams known as maximal length Pseudo Random Binary Sequences' (hereinafter referred to as PRBS), which may be formed by serializing a plurality of parallel streams.
The bit rate of a serial stream formed as above is typically an order of magnitude higher than that of the parallel streams from which it is formed. Such serial 16 streams are used, for example, in the testing of high speed digital signal links. There is a need to provide a means of producing a trigger signal which is synchronized to the high rate serial stream and which occurs in the same position during each repeating pattern.
One way of producing such a trigger signal would be to sense a particular sequence of bits in the serial stream. This would require logic circuitry operating at the high (serial) rate, and would be complex.
An alternative is to try to sense a sequence of bits occurring in the parallel stream. This would not necessarily give one trigger signal for each repetition of the serial output pattern.